1. Field of the Invention
This invention relates to a skiving cutter for use in cutting an internal spur gear.
2. Description of the Prior Art
For easier and better understanding of this invention, a conventional gear skiving or cutting process will be described below with reference to FIGS. 1 to 3 of the accompanying drawings.
As shown in FIGS. 1 and 2, a cutter gear having cutting blades "a" formed along the stagger axis, that is, helical pinion cutter "b" is used which is forcibly moved in the direction as indicated by the arrow as a fly cutter rotated within a vacant space for skiving the work peice "c" to be cut by the line of cutting blades thereof to form an internal spur gear. This work process is highly efficient, but since it has frequently caused the staggered contact between the cutter "b" and the work piece "c" to be cut, analyzed design procedures thereof were troublesome. Therefore, the analysis thereof were insufficient and unsatisfactory.
In order to achieve the sufficient skiving operation, an arrangement should be made such that the contacting point between one of cutting blades "a" and a work piece "c" to be cut is located at a pitch point P between the cutter and the workpiece to be cut. If the contacting point is located away from the pitch point P, the tooth profiles along the left and right sides formed on the work piece "c" become unsymmetrical, and thus an offset cutter could not be used. As a consequence, the effective width "l" of the cutter is limited by the side clearance angle .delta. thereof and so the number of regrinding cutting blades is limited as well.
Of late, the gear skiving or cutting process has been theoretically analyzed and an interference diagram as shown in FIG. 3 has been obtained based on the theoretical analysis values. In FIG. 3, reference characters C.sub.1d and C.sub.1r denote respective interference lines at the root and bottom of the teeth cut on the work piece "c" and C.sub.2k an interference line at the addendum of the cutter "b". The part encompassed by the interference lines C.sub.1r, C.sub.1d and C.sub.2k or the region indicated by oblique lines is defined to be a contact or action region L. Therefore, it can be seen that if the gear is designed such that the contacting point between the cutting blades of the cutter "b" and the work piece "c" to be cut is located within the contact or action region L, it becomes possible to obtain an accurate symmetrical tooth profile along the left and right sides formed on the work piece "c" even though a design value Po of cutting blade profile of the cutter is offset downwards for the contacting point.